High frequency apparatus



June 17, 1941. Y J. P. BLEWETT HIGH FREQUENCY APPARATUS Filed W 24, 19402 Sheets-Sheet 1 Fig. l.

Inventor: John P. Blewett,

by A! His ttorney.

June 17, 1941. J, ,5. BLEWETT 2,246,121

HIGH FREQUENCY APPARATUS Filed May 24, 1940 2 Sheets-Sheet 2 Fig. 4.

Inventor: John P. Blewett,

His Attorney.

Patented June 17, 194i 2.240.121 HIGH momcrsrmna'rus John P. Blewett,eral Electric York Bootla, N. Y.I assignor to Gen- Oompany, acorporation of New Application May 24, 1940, Serial No. 337,043

6 Claims. (Cl. 179-171) The present invention relates to improvements inelectronic apparatus for use at ultra-high frequencies.

The invention makes use of so-called velocity modulation principleswhich are described in Patent 2,220,839, granted November 5, 1940 in thename of W. C. Hahn. It is a primary object of this invention to providea novel and compact tube structure in which such principles may beapplied. To this end use is made of a flattened, relatively wide andlong chamber through which a stream of charged particles is caused tomove along a path of generally trochoidal character. By this means. oneis enabled to provide a stream path of relatively great length and toachieve amplification effects depending upon this factor in spite of theuse of a very compact tube structure.

The features which I desire to protect herein are pointed out withparticularity in the appended claims. The invention itself, togetherwith further objects and advantages thereof, may best be understood byreference to the following description takenuin connection with thedrawings in which Fig. l is a longitudinal view in partial section of adischarge device suitably embodying the invention, Fig. 2 is across-sectional view taken on line 2-2 of Fig. 1. Fig. 3 is across-sectional view taken on line 2-3 of Fig. l, and Figs. 4 and 5 arediagrammatic representations useful in explaining the invention.

Referring particularly to Fig. 1, there is shown a relatively elongatedenvelope which has a flattened cross-section as indicated in Fig. 2.Within the envelope there are provided a plurality of conductive parts,numbered I I to 14 inclusive, which conjointly define a hollow chamberof flattened configuration. These conductive parts, the relationship ofwhich is best shown in Figs. 2 and 3, are mutually insulatingly spacedso as to provide gaps I6 and I! which extend parallel to thelongitudinal axis of the envelope. The extremities of the parts adjacentthe ends of the envelope III are preferably closed by means oftransverse wall portions (not shown) so that the chamber defined by theparts is of substantially completely enclosed character.

At one end of the envelope, there is provided an electron gun 20. Thisis not illustrated in detail, but it will be understood that it maycomprise a cathode and one or more focusing and accelerating electrodesserving to produce an electron stream. The cathode element of the gun ismaintained at an appropriate negative potential by means of a battery2land the axis of the gun is so directed that the initial path of thestream produced thereby is transverse to the principal axis of theenvelope.

In accordance with my present invention the electron stream thusproduced is caused to move longitudinally through the chamber formed bythe parts ll-ll along a path which is of generally trochoidal character.This may be accomplished in one way by the use of a magnetic fieldhaving its flux lines extending parallel to the short dimension of thechamber, such a field being produced. for example, by a U-shapedmagnetic structure indicated at 22. 'It will be understood that it isthe function of the magnetic structure to transform the linear motion ofthe electrons projected from the gun 2| into orbital motion by theaction of its magnetic field. The magnetic structure may be excited bymeans of a coil 22, i

In order to assure progressive motion of the axis of -gyration of eachelectron in a direction parallel to the long dimension of the envelopeIII, a unidirectional potential is applied between the conductive partl3 and the parts II and I2 which are in juxtaposition thereto. Thispotential is provided, for example, by means of a battery 24 which isshown as being connected directly to the part 12 and indirectly to thepart II through a choke coil 25. The potential is in such a direction asto produce a positive gradient acting on the electrons as they leave theconfines of the conductive part I3 and traverse. the gap it. As a resultof this gradient, the velocity, and consequently the radius of gyration,of any given electron tends to increase as the electron leaves the partl3. On the other hand, since the same electron is decelerated at the gapii at the instant when it next enters the gap (1. e. upon leaving thepart ii) its radius of gyration will be again diminished. As aconsequence of this action, which is repetitive for each passage of theelectron across the gap I6, the forward movement which the electronexperiences in the upper half .of its orbit will be less than theregressional movement which occurs in the lower half of the orbit, and aresultant progression of the electron will occur, as indicated by thedotted line 26 of Fig. 1. The various elements of the electron streammay be collected on the end walls of the signal input source 21. As aresult of the variable potential gradients produced in this manneracross the gap II. the various electrons which traverse the gap will bedifferently ail'ected in velocity depending upon the part of thepotential cycle at which they reach the gap. Specifically, certainelectrons will be accelerated above the average stream velocity andothers will be decelerated below such average velocity. Consequently,the beam will become velocity modulated in the sense of having recurrentvariations in velocity from point to point along the beam path.

With a structure such as that shown it is apparent that each electron iscaused to traverse the gap II a number of times. Consequently, if theaverage orbital transit time of the electrons is correlated to.thefrequency of the input signal applied from the voltage source 21, thevelocityvarying effects experienced by a given electron may be madecumulative for each traversal of the 88p. In the case illustrated,wherein the orbital path of the electrons is controlled by means of auniform magnetic field, little difilculty is experienced in assuring adesired correlation between the orbital transit time of the electronsand the rate of potential variation of the input signal. This is due tothe fact, demonstratable mathematically, that the time required for thevarious electrons to complete a single orbital turn is controlledexclusively by the strength of the magnetic field and is independent ofthe electron velocity. Consequently, for a given field strength,

irrespective of the velocity with which a given electron may leave thegap it, itwill return to the gap within a fixed and invariable time.Therefore, if the strength of the magnetic field is properly adiusted tocause the time of orbital transit of each electron to correspond to somewhole number of cycles of the operating frequency, the efiect of theinput system upon such electron will be additive for each of itssuccessive traversals of the gap.

The matters referred to in the preceding paragraph may be more clearlyunderstood by referring to Fig. 4. In this figure the solid line B maybe taken to represent the path of a circularly moving electron whosevelocity corresponds to the average or unmodulated velocity of theelectron stream of which it forms a part. The point is considered torepresent a region at which the stream is subjected to a high frequencymodulating potential.

An electron which passes the modulating agency in such time phase as tobe accelerated thereby, may be expected to follow a path of somewhatgreater radius than the path 13, such enlarged path being represented,for example, by the dotted line C. 0n the other hand, deceleratedelectrons will describe a smaller orbit, as indicated by the dotted lineD. Theoretical analysis shows, however, that each electron will requireprecisely the same time to traverse its orbit and return to the point 0.

In order to understand the possibility of obtaining amplificationeffects as a result of the considerations discussed in the foregoing, itwill be helpful to refer to the action of a circularly moving electronstream which is caused to travtime a modulating gap at which it issubjected to cyclically varying potential gradients. This situation isillustrated diagrammatically in Fig. 5, which may be taken to show theconditions existing at various points around the orbit of an electronstream which is caused to traverse a s earer modulating gap at O". Forthe case illustrated it is assumed that the frequency of potentialvariation across the gap is such that eight complete cycles of variationoccur during the time required for a single electron to traverse itsorbit. The small circles a may be taken to represent individualelectrons, and, considered in the aggregate, they show the condition ofthe beam at a particular instant of time. As the various electrons moveorbltally, those whose velocity exceeds the average beam velocity, seekan orbit of greater radius, while the decelerated electrons seek anorbit of reduced radius. As a consequence of this action, observationstaken between various closely spaced azimuthal planes will show that theelectron density measured at most points aroundthe electron path variesmaterially with time. This variation is mainly a function of therelative displacement of the centers of gyration of the variouselectrons and is found to be greatest between planes which are locatedapproximately ninety mechanical degrees from 0'', such planes beingindicated at b and b. It will be noted that at the instant which isrepresented in Fig. 5, considerable bunching of the electrons existsbetween the planes b-b at the upper side of theelectron orbit, while arelative paucity of electrons exists between the same planes at theopposite side of the orbit. 0n the other hand, this situation would befound to be reversed at an instant taken a half-cycle later. It is,therefore, apparent that on either side of the electron orbit theportion of the beam between the planes b-b' will be characterised by theoccurrence of charge density modulation, that is, cyclical variation ofelectron density'with time. While the charge density modulation observedbetween the planes H is variable with the velocity modulation whichproduces it, it may, under practically attainable conditions, be of ahigher order of magnitude; that is, even relatively slight velocitymodulation produced at the gap 0" may be made to cause relatively greatcharge density variations in the region b-b'. Therefore, if some meansare provided by which the charge variations at b-b' can be utilised inanappropriate manner, the system as a whole may be employed foramplification purposes.

In order to make use of the above-described phenomena in connection withthe apparatus of Fig. 1, an output circuit comprising the parallelcombination of an inductance 3| and a condenser il may be connectedacross the gap H which separates the conductive parts I! and II. It willbe noted that this gap intercepts the various electron orbits at pointsapproximately ninety degrees displaced from the points of theirtraversal of the gap it. Therefore, for the reasons given in connectionwith the disclosure of Fig. 5. velocity variations produced by the gapll will produce corresponding charge density variations in the portionof the stream which traverses the gap ll. These variations will, inturn, induce currents in the conductive parts It and I4 and thus causeexcitation of the output circuit 3|, ii. The output mechanism thusprovided is especially effective due to the fact that each element ofthe electron stream repetitively traverses the gap i'l. Consequently,each electron of the stream has an opportunity to aflect the outputstructure a number of times. With a proper adjustment of the orbitalvelocity of the stream ttliihs1 egrill result in cumulative elects beingob- While the invention has been described in connection with a pureelectron discharge, it is considered to be equally applicable inconnection with other types of charged particles, such as positively ornegatively charged ions. Moreover, the particular structure illustratedis in no way essential to the practice of the invention, and I aim inthe appended claims to cover all such equivalent variations of structureas come within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In combination, means for generating a stream of moving charges,means for causing the stream to follow a path of generally trochoidalcharacter, modulating means acting on the stream at an initial portionof its path to produce high frequency variations in the stream velocity,and means coupled to a portion of the stream previously afiected by thesaid modulating means for abstracting energy therefrom.

2. In combination, means for generating a stream of electrons, means forcausing the various electrons in the stream to follow paths of generallytrochoidal character, modulating means acting on the stream at a pointrelatively near its origin to produce high frequency variations inelectron velocity, and means coupled to the stream at a point relativelymore remote from its origin for abstracting high frequency energytherefrom.

3. In combination, means for generating a stream of electrons, meansdefining a flattened, relatively wide and long chamber to be traversedby the stream, means including a magnetic-fieldproducing structure forcausing the said stream to move longitudinally of the chamber along apath of generally trochoidal character, means acting on the stream at apoint relatively near its origin for producing high frequency variationsin the electron velocity, and means coupled to the stream at a pointrelatively more remote from its origin for abstracting high frequencyenergy therefrom.

4. In combination, a gas-tight envelope defining a flattened, relativelywide and long enclosure, means for generating a stream of chargedparticles and for causing the said stream to move longitudinally of theenclosure along a path of generally trochoidal character, spacedconductive members with the envelope defining a gap in proximity to thestream path; means for impressing a cyclically varying potential betweenthe said members to produce high frequency variations in the velocity ofthe components of the stream which successively pass the gap, and outputmeans for abstracting energy from the stream after-its passage of thesaid gap.

5. In combination, means for generating a stream of moving charges,conductive parts defining a flattened, relatively wide and long chamberwhich is traversed by the stream, certain of the said parts whichcomprise the principal lateral walls of the chamber being insulatinglyspaced to provide a narrow gap which extends longitudinally of thechamber, means for apply.- ing cyclically varying potentials between theparts which bound the said gap, means for causing the said stream tomove longitudinally of said chamber along a generally trochoidal pathwhich passes in proximity to the said gap, and output means excited byvariations which exist in the said stream after it has passed the saidgap.

6. In combination, means for generating a stream of moving charges,conductive parts defining a flattened, relatively wide and long chamberwhich is traversed by the stream, certain of said parts beinginsulatingly spaced to deflne at least two mutually ofiset gaps whichextend longitudinally of the principal lateral walls of the chamber,means for causing the said stream to move longitudinally of the chamberalong a generally trochoidal path which passes in proximity to the saidgaps, means for applying a high frequency input potential between theconductive parts which deflne one of said gaps, and output meansconnected acrossthe other of said gaps and adapted to be excited by thevariations produced in the said stream by the said input potential.

JOHN P. BIEWEIT.

